An analytical model to study of potential effects on component elongation in shot peening

Shot peening (SP) is widely used in aerospace factories and automotive enterprise for large thin panel forming and strengthening, such as the wing skin panels, spars, and car bonnet. The large panels or sheets are subjected to SP processing, followed by the bending, spanning, and growth (elongation). Precise elongation calculation is a promising and challenging task. This work which includes the mathematical model finite element method (FEM) simulation for predicting the 7050-T7451 aluminum alloy strip elongation with respect to special SP parameters is presented to analyze the potential effects, which was also validated by experiments. As to the integral wing spars, the rolling direction orientations with regard to the rolled spar blank have different effect on elongation after the SP strengthening and shaping. The compressive stress induced by SP will break the original residual stress equilibrium state after rolling. Both experiments and explicit-implicit model predictions showed that the tensile residual stress induced by rolling contributes to the elongation. On the contrary, the compressive residual stress prevents the strip from elongation. Furthermore, the initial residual stress effect is negligible when the thickness is large (above 6-mm thickness). Considering the 7050-T7451 aluminum alloy coefficient of thermal expansion is high, therefore, the temperature is an important factor for the long length spar. In addition, we found the elongation was inversely proportional to thickness and independent of section dimension. The numerical results showed that the elongation was more sensitive to the shot number (coverage) than impact velocity, which was explained based on the newly proposed mathematical model.